This invention relates generally to devices for producing axial thrust by rotation in a fluid such as air or water. More particularly, the present invention relates to a rotatable circular foil designed to create an imbalance of fluid pressure acting on opposite faces of the circular foil to cause it to move in the direction of the deficit.
Devices for producing axial thrust by rotation in a fluid such as air or water and which have received an almost universal application are in the form of the so-called screw propellers. Screw propellers are generally designed on the basis of the characteristics of the particular fluid environment in which they will be used, and are widely used for aircraft and marine propulsion.
Generally, screw propellers for marine use are of considerably smaller diameter than propellers used for aircraft for absorbing comparable power and may have more blades than the aircraft propellers. Three-blade propellers have now become particularly popular for larger aircraft, while four-blade propellers have been extensively used for marine propulsion, particularly for larger craft.
The axial thrust produced by a screw propeller depends upon the degree of vacuum created on the surface of the blade on the side of the direction of its travel because of movement of the blade through the fluid at a certain angle to the general plane of rotation of the blade, and on the area of the blade at which such partial vacuum or reduced pressure is caused to act. The faster the rotation of the propeller blades, the greater is the degree of vacuum so created. Also, the greater the number of the blades on the propeller, the greater is the area at which fluid pressure acts to produce axial thrust.
However, limitation for both of the above factors exists in the fact that increase both in the speed of rotation and/or in the number of the blades beyond a certain limit, determined primarily by the nature of the fluid, causes rarification of the fluid to such an extent that in spite of increase in the degree of vacuum, the fluid pressure from the opposite side begins to decrease in a degree nullifying the beneficial effect of the increased vacuum. Therefore, limitation in the number of propeller blades, usually to three or four, determines the maximum area at which the fluid pressure acts on the propeller and, therefore, determines the total axial thrust produced thereby. In the case of aircraft propellers having three blades, such area may be equal, in effect, to only approximately 15% to 20% of the total circular area determine by the radius of the propeller.
In view of these limitations, propeller devices have been proposed which attempt to increase the effective area on which fluid pressure acts for producing the axial thrust, as compared with screw propellers, whereby a much greater total axial thrust is produced without increasing the overall radius of the propeller mechanism. An example is found in U.S. Pat. No. 3,124,200 to Everett E. Wilson. The propeller device disclosed therein includes, generally, a flat circular plate and a number of blades or fins extending upwardly from the plate generally from the center of the plate to its circumference, which blades or fins are generally inclined at an angle to capture fluid during rotation of the plate and create an axial lift-producing force. The blades or fins are arranged on the flat circular plate to encourage an evacuation of the fluid from the front surface of the plate as it is rotated to create a thrust-producing pressure imbalance.
Such disc-like alternatives to the standard screw propeller have not found wide acceptance. Although, theoretically, they should produce as much or greater thrust in an axial direction than screw propellers, prior disc propeller designs have failed to realize their full potential.
Accordingly, there has been a need for a novel rotating thrust-producing apparatus which is of simple construction, overcomes noted drawbacks of prior propeller mechanisms, and which is adaptable for use in most fluid environments. Additionally, a novel rotating thrust-producing apparatus is needed which is capable of causing a pressure reduction on an upper face of a flat circular plate while maintaining a lower face thereof at its original pressure to thereby form a pressure imbalance which causes the apparatus to move in the direction of pressure reduction. Moreover, such an improved apparatus is needed which effectively creates a vacuum over a portion of a rotating plate to realize the desired thrust and also to reduce drag on the apparatus itself. The present invention fulfills these needs and provides other related advantages.